Photochemical aerosol formation in sulfur dioxide-hydrocarbon systems.

Abstract

We have conducted a series of photochemical experiments in a 50 to 1 stirred-flow to study aerosol formation from different hydrocarbons in the presence of nitrogen oxides and sulfur dioxide. Irradiation by simulated sunlight of trace concentrations (p.p.M.) of the reactants, in some cases, yielded particles in the size regime 0.1-0.3 micrometers diameter, which by scattering of light are important to visibility in the atmosphere. A large number of experiments with 3 p.p.M. SO/sub 2/ indicated that the olefinic hydrocarbons were the only important aerosol formers in contrast to the paraffinic and aromatic hydrocarbons. It was observed that the photolysis of sulfur dioxide proceeds at the rate of 0.4 percent per minute. The high sulfate content of the particulate matter and low gaseous sulfur dioxide concentrations observed in the Los Angeles smog are consistent with the findings of this laboratory program.